In model systems composed initially of lysozyme and oxidizing methyl linoleate, but possibly in systems with other proteins, we shall seek to answer the following questions: a) Is there formation of free radicals on the protein? b) If yes, what are the preferred sites for this formation? c) What are the necessary conditions for free radical formation, in particular what is the effect of water activity? d) What are the preferred subsequent reactions of these radicals? In model systems containing amino acids, peroxidizing methyl linoleate, and other components analogous to pro- and anti- oxidants occurring in foods we shall seek to isolate, identify and quantify amino acid-derived oxidation products. In foods and in selected tissues experiments will be conducted to confirm the existence of mechanisms established in model systems. Selected experiments will study the role of biological and synthetic anti-oxidants, and of natural and added pro-oxidants. The overall objective of this research is the understanding of mechanisms and conditions of occurrence of interactions between peroxidizing lipids and other food constituents, notably proteins, amino acids, and vitamins. The further aim is the utilization of this knowledge for minimizing undesirable changes and preventing changes leading to formation of toxic compounds and of antimetabolites. The proposed work will concentrate on interactions occurring in systems simulating dehydrated, intermediate moisture and frozen foods, but the proposed work has implications for other biological systems.